Changes in corticospinal excitability during reach adaptation in force fields

Abstract

Both abrupt and gradually imposed perturbations produce adaptive changes in motor output, but the neural basis of adaptation may be distinct. Here, we measured the state of the primary motor cortex (M1) and the corticospinal network during adaptation by measuring motor-evoked potentials (MEPs) before reach onset using transcranial magnetic stimulation of M1. Subjects reached in a force field in a schedule in which the field was introduced either abruptly or gradually over many trials. In both groups, by end of the training, muscles that countered the perturbation in a given direction increased their activity during the reach (labeled as the on direction for each muscle). In the abrupt group, in the period before the reach toward the on direction, MEPs in these muscles also increased, suggesting a direction-specific increase in the excitability of the corticospinal network. However, in the gradual group, these MEP changes were missing. After training, there was a period of washout. The MEPs did not return to baseline. Rather, in the abrupt group, off direction MEPs increased to match on direction MEPs. Therefore, we observed changes in corticospinal excitability in the abrupt but not gradual condition. Abrupt training includes the repetition of motor commands, and repetition may be the key factor that produces this plasticity. Furthermore, washout did not return MEPs to baseline, suggesting that washout engaged a new network that masked but did not erase the effects of previous adaptation. Abrupt but not gradual training appears to induce changes in M1 and/or corticospinal networks.

Interactions Among Learning Stage, Retention, and Primary Motor Cortex Excitability in Motor Skill Learning

“…If the M1 stores motor memory, changes in M1 excitability induced by motor skill learning will be associated with retention of learned motor skills. Previous study demonstrated that LTP-like plasticity is essential for performance retention [48,49]. In the present study, a reduction in the performance score during the first two blocks performed on Day 2 only occurred in the SSL group.…”

Observing object lifting errors modulates cortico-spinal excitability and improves object lifting performance

“…In support of this idea, (Alaerts et al, 2011) have shown that, in a blocked design, visual information about object weight from previously observed lifts drives cortico-spinal excitability before visual information about object weight in an upcoming observed lift is available. These low-level modulations may even serve a behavioural function, given the growing experimental evidence for a link between cortico-spinal excitability and motor output (Bagce et al, 2013;Klein-Flügge et al, 2013;Orban de Xivry et al, 2013). In the context of object lifting, Loh et al, (2010) have provided strong evidence that cortico-spinal excitability is related to fingertip force scaling by demonstrating that, in the same individuals, the ratio between MEPs before lifting for heavy and light objects correlates with the ratio for the force rates used to lift the same heavy and light objects.…”

Contributions of the cerebellum and the motor cortex to acquisition and retention of motor memories

“…Formation of this motor memory appears independent of human medial temporal lobe structures (Shadmehr et al, 1998), but dependent on the integrity of the cerebellum (Smith and Shadmehr, 2005; Criscimagna-Hemminger et al, 2010; Donchin et al, 2012), and the motor cortex (Li et al, 2001; Richardson et al, 2006; Arce et al, 2010b; Orban de Xivry et al, 2011b; Orban de Xivry et al, 2011a; Orban de Xivry et al, 2013). In particular, a study in humans demonstrated that reversible disruption of the thalamic projections of the cerebellum to the cortex produced within-subject impairments in the ability to learn the force field task (Chen et al, 2006).…”